login_hint is an optional parameter in openid Authorization Grant. https://gluu.org/docs/gluu-server/4.1/api-guide/openid-connect-api/#parameters_1 I found this old issue, which is fixed ages ago, suggesting that it should work: https://github.com/GluuFederation/oxAuth/issues/120 I've switched the primary key from uid to mail. https://gluu.org/docs/ce/4.2/operation/faq/#request-email-instead-of-username-for-login If I pass a valid email address via login_hint it does not appear in the custom login page (the only change I've made is to switch the label 'username' for 'email address' as suggested). what I don't understand is: - is login_hint implemented? - does it work with primary key mail? - does it work with authentication method casa? - does it work with custom login pages? my GET URL looks like this: https://gluu.mydomain.com/oxauth/authorize.htm?login_hint=testah%40mydomain.com&scope=openid+profile+email&response_type=token&redirect_uri=https%3A%2F%2Fweb2012.mydomain.local%2Fwebtools%2Fcustomer%2FLogin.aspx&state=820649e7-a0db-4b95-971d-62e6ed7bca50&nonce=86f97528-d914-4f97-af9b-048585610fd8&client_id=7ef24196-3b95-4380-b593-98e300069421&response_mode=form_post Any help appreciated